A piston ring used in an internal combustion engine of a motor vehicle or the like is provided in, for example, a ring groove of a piston outer peripheral surface, and has a function of restraining oil on a cylinder inner wall from entering a combustion chamber side from a crank chamber side (oil-up), and restraining blowby gas from entering the crank chamber side from the combustion chamber side. Examples of the piston ring having such a function include a piston ring described in Patent Literature 1. This conventional piston ring is also called a second ring, and has a tapered section provided on an upper surface side in an outer peripheral surface, and a flat section parallel to the axial direction of a piston. A corner section formed by the tapered section and the flat section, and a corner section formed by the flat section and a lower side surface each have a rounded shape.